Pulse forming circuit



W. B. VARNUM PULSE FOBMING CIR'CUITA Filed Dec. 31, 1943 Pini Nov. 4, 1947.

MUSS, Wx vx; SSW

vlar rom/Y Patented Nov. 4, 1947 2,430,315 PULSE FORMING CIRCUIT Walter B. Varnum,

Collingswood, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application December 31, 1943, Serial No. 516,426

(Cl. Z50-27) Claims.

My invention relates to the production of electrical pulses particularly for use in radio pulse-echo systems.

An object of the invention is to provide an improved method of .and means for producing electrical pulses. v

A further object of the invention is to provide a. simplified pulse producing circuit.

A still further object of the .invention is to provide an improved circuit for triggering a selfpulsed oscillator.

In one preferred embodiment of the present invention a sine vwave voltage is applied to the anode and grid electrodes of a gas or vapor tube,

fie voltage applied to the grid being delayed by about 90 degrees for example. As a result, the tube breaks down (is ignited) Lso that the voltage at the tube anode has a wave form with a steep or nearly vertical slope. The voltage of this wave form is applied to the grid of a vacuum tube that has an inductance coil in its plate circuit whereby the current flow through the inductance coil builds up during about one-fourth of the sine wave cycle and then collapses suddenly upon the occurrence of the steep portion of the said wave form. This sudden collapse is due to the fact that the Vacuum tube is driven to plate current cut-off at this instant and will be explained hereinafter. Thus a voltage pulse is produced across the inductance coil. This voltage pulse is utilized, in the particular example described herein, for triggering a self-pulsed radio-frequency oscillater.

The invention will be better understood from the following description taken in connection with the accompanying drawing in which the single figure is a circuit diagram of one embodiment of the invention.

Referring to the drawing, a sine Wave voltage I0 having the frequency of the desired pulse repetition rate is supplied from a suitable source II to an amplifier tube I2. The amplified Wave IIJ is 'applied through a blocking capacitor I3 and a resistor I4 to the anode I6 of a grid controlled gas or vapor tube I1 such as a Thyratron which will not ignite or break down until a certain ratio exists between the voltage on the anode I6 and the voltage on the control grid I8. The cathode I9 of the tube I'1 is grounded.

The sine wave Il) is applied to the grid I8 through a phase shift or delay circuit comprising resistor-capacitor sections 2 I--24 and 22--26 and through a grid current limiting resistor 23. The amount of delay introduced is such as to make the tube I1 ignite at about rthe time the voltage on the anode I6 is amaxirnum. The resulting voltage on the anode I6 has the wave form shown by the graph 21. It will be noted that this voltage wave has a steep portion 21 which is produced at the instant of ignition of the tube I1.

The anode I6 is coupledr through a capacitor 3I to the control grid 32 of a vacuum tube 33. A suitable negative bias (-C) may be applied to the grid 32 through a filter resistor 35 and a grid leak resistor 46. A filter capacitor is shown at 35. The tube 33 may be a pentode having a directly heated cathode 34, an anode 36, a suppressor grid 31, a screen grid 38 land the control grid 32. Filament heating current is supplied to the cathode 34 through a transformer 39. A center tap .on the secondary of transformer 39 is connected to ground through a resistor 4I of cnly a few ohms resistance that is provided so that an oscilloscope may be connected thereacross to observe the wave form of the tube current. Resistor 4I is bypassed by a capacitor 42.

The D.-C. operating voltage (+B) is applied to the anode 36 through a choke coil 43 across which there will appear a voltage pulse 44 when the current flow therethrough is suddenly interrupted.

The operation of the circuit in producing the pulse 44 is as follows:

The voltage wave 21 is of suiiicient amplitude to drive the grid 32 of the tube 33 positive whereby there is a flow of grid current as the wave 21 increases in amplitude. This grid current charges the coupling capacitor 3l. At the instant the vapor tube I`1 breaks down to produce steep wave portion 21', the anode-to-cathode impedance of tube I1 becomes very small so that the capacitor 3l is eiectively connected between the control grid 32 and the cathode 34 of the tube 33. Therefore, the charge on capacitor 3l instantly biases the tube 33 beyond anode current cut-ofi and the anode current that has been owing through the choke coil 43 is suddenly interrupted whereby the voltage pulse 44 is produced.

As soon as the vapor tube I1 deionizes, its impedance becomes so high, that it is practically an open circuit and the voltage of capacitor 3I is no longer applied between the cathode 34 and grid 32. However, the negative portion of the wave 21 now holds .the tube 33 at plate current cut-oli until on the next cycle of the wave 21 the instantaneous voltage increases suiciently to permit anode current oW through the choke coil 43 again. As the instantaneous value of the wave 21 rises further, the value is reached where there is the aforementioned grid current now which charges the capacitor 3 I, and then near the maximum voltage of wave 21 the tube I1 ignites vto 3 produce the next pulse "54, The current iiow through the tube 33 and choke coil 43 during the above described operation is shown by the graph 46. A resistor 4i' may be connected between ground and the junction point of capacitor I3 and resistor l in order to provide a path through which the charge on capacitor 3| may continue to leak oir after the tube I'l has deionized and to provide a direct-current connection from the grid of vapor tube Il to ground.

In the example illustrated, a pulse-forming delay line or network 5i is employed to control the duration of a pulse 52 of radio-frequency energy which is produced by a self-pulsed oscillator 53. The pulse is applied to the grid of the oscillator 53 and to one end of the network 5l through a blocking capacitor Sii. The network 5l comprises series inductors 5in and shunt capacitors Sib. The pulse ell triggers the oscillator 53 and at the same time a pulse of oscillator grid current travels down the network 5l to the open end where it is reected back. The reilected voltage from the network 5i blocks the oscillator 53 whereby there is produced the R.-F pulse 52 having a duration equal to the time required for a voltage Wave to travel down the network 5I and back.

The oscillator 53, which is indicated only schematically in the drawing, may be of the type described in application Serial No, 460,670; filed October 3, 1942, in the name of Carroll D. Kentner, and entitled Multi-tube self-pulsing transmitter. This particular oscillator is of the tuned grid-tuned cathode type and is adjusted to selfpulse or block at a lower frequency than the one desired. This adjustment of the self-blocking time is made by adjusting a grid resistor 55. The triggering pulses l-lll then control the pulsing rate of the oscillator exactly,

From the foregoing it will be apparent that I have provided a simple and eective pulse producing circuit, and that I have also provided an improved circuit for triggering a self-pulsed oscillator.

I claim as my invention:

l. An electrical pulse producing circuit cornprising a vacuum tube having an anode, a grid and a cathode, an inductance coil through which a direct-current voltage is applied to said anode, a gas or vapo tube having an anode, a control electrode and a cathode, means for applying a periodic voltage to the anode or said vapor tube, means for applying a periodic voltage to said control electroue to ignite said vapor tube after the instantaneous voltage on the anode of the vapor tube reaches e, substantial value, and means including a coupling capacitor for coupling the anode and cathode of said vapor tube to the grid and cathode of said vacuum tube, respectively, the voltage applied to the control grid of said vacuum tube having sufficient amplitude to drive said control grid positive whereby said coupling capacitor is charged by a dow of grid current and wiiereb i vacuum tube is driven to anode curn when said vapor tube ignites thereby producing a voltage pulse across said inductance coil.

`:uise producing circuit com- .ce having anode, a grid Luctance coil through which tage is applied to said anode, a or l tube having an anode, a control electrode a cathode, means for applying a sine wave voltage to the anode of said vapor tube,

means for applying a voltage to said control electrode to ignite said vapor tube after the instantaneous voltage on the anode of the vapor tube reaches a substantial value, and means including a coupling capacitor for coupling the anode and cathode of said vapor tube to the grid and cathode of said vacuum tube, respectively, the voltage applied to the control grid of said vacuum tube having sumcient amplitude to drive said control grid positive whereby said coupling capacitor is charged by a now of grid current and whereby said vacuum tube is driven to anode current cutoi when said vapor tube ignites thereby producing a voltage pulse across said inductance coil.

3. An electrical pulse producing circuit comprising a vacuum tube having an anode, a grid and a cathode, an inductance coil through which a direct-current voltage is applied to said anode, a gas or vapor tube having an anode, a control electrode and a cathode, means for applying a sine wave voltage to the anode of said vapor tube, means for applying a voltage to said control electrode to ignite said vapor' tube after the into the grid and cathode of said vacuum tube, respectively, said coupling means including a capacitor connected between the anode of said vapor tube and the grid of said vacuum tube, the voltage applied to the control grid of said vacuum tube having sufficient amplitude to drive said control grid positive whereby said coupling capacitor is charged by a flow of grid current and whereby said vacuum tube i driven to anode current cut-off when said vapor tube ignites thereby producing a voltage pulse across said inductance coil.

1i. An electrical pulse producing circuit coma cathode, an inductance coil a direct-current voltage is applied a gas or vapor tube having an anode, a control electro-de and a cathode, means for applying a sine Wave voltage to the anode or" said vapor tube and to said control electrode with the sine Wave voltages on said anode and said control electrode out of phase whereby said vapor tube ignites after the inst. taneous voltage cn the anode of the vapor tube reaches a substantial value, and means inclu-` ng coupling capacitor for coupling the anode and cathode of said vapor tube to the grid and cathode of said vacuum tube, respectively, the voltage applied to said control grid having suiiici :t amplitude to drive said control grid posit've w ereby said coupling capacitor is charged by a flow of grid current and whereby said vacuum tube driven to anode current cutoff whe' said vapor tube ignites thereby producing a vo tage puise across said inductance coil.

5. An electrical pulse producing circuit comprising a vacuum tube having an anode, a grid and cathode and having an anode circuit and a grid circuit, an inductance coil in said anode circuit through which the anode current of said tube flows, a gas electrode and having an anode coupled to said grid circuit nrough a capacitor and also having a cathode connected to the cathode of said to said anode,

voltage to the anode of said vapor tube and to said control electrode with the voltage on said control electrode delayed.

W'ALTER B. VARNUM. 

